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1 ENS. 1 ' . Mr James L Barton ' January 26, 2005 Page 4 1 ' Remediation System Description The remediation system consists of an Air Sparge / Soil Vapor Extraction (AS/SVE) system The AS system includes an air compressor with a maximum positive displacement of 95 ' standard cubic feet per minute (scfm) and a maximum pressure of 125 pounds per square inch (psi) that is manifold to 13 air sparge wells The system sparges contaminant-free air into the subsurface saturated zone at rates between approximately 10 0 and 58 0 scfm, enabling a ' phase transfer of hydrocarbons from a dissolved state to a vapor phase The air is then vented through the unsaturated (vadose) zone The sparge wells are manifold to the system by Schedule 40 polyvinyl chloride (PVC) The flow rate for each sparge well can be manually adjusted to optimize the system Additionally, each sparge well is equipped with ports that allow for the monitoring of air flow rates and pressure The SVE system includes a thermal oxidizer with a 1,000,000 British Thermal Units (BTU) burner and a positive displacement vacuum compressor rated at 400 scfm The approximate operating vacuum is 80 inches of H2O A vacuum is applied through thirteen soil vapor 10 extraction extraction wells, and four groundwater monitoring wells near the previously identified sources of contamination to the vadose zone sod Extracted vapor is treated using the thermal oxidizer before being released to the atmosphere The system is operated under San Joaquin Valley Air Pollution Control District (SJVAPCD) Permit Number N-5879-1-0 SVE wells are manifold to the system by Schedule 40 PVC piping The flow rate for each extraction well can be manually adjusted to optimize the system Additionally, each extraction well is equipped with ports that allow for the monitoring of air flow rates and or pressure Well construction details are in Attachment C and the system layout is shown in Figure 15 ISoil Vapor Extraction System Status I The SVE system was started to October 1999 as required by CAO No 5-00-707 The SVE system was shut down in October 2003 as a result of "a general downward concentration trend for all wells, including MW-11 and MW-12, with occasional spikes" as stated in the RWQCB letter dated October 23, 2003 The SVE system was restarted on September 24, 2004, with RWQCB approval, as a result of an increase in the size of the benzene plume in the B-zone between the fourth quarter 2003 and third quarter 2004 On November 30, 2004, ENSR discovered a hole in the outside wall of the thermal oxidizer combustion chamber On December 7, 2004, ENSR submitted a letter to the RWQCB that provided an assessment of recent events concerning the interruption of the SVE system operation and a detailed schedule of steps that will be taken to restart the SVE system J 1Protects10694015098-2931WorkmglReports15098 4th Qtr 04-QMR doc �r Celebrating 35 Years of Excellence to Environmental Services